Why remote desktop tools are facing an onslaught of cyber threats

Cartoon cloud connected to nine separate computers shown as folder icons indicated remote desktop tools
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In the era of hybrid work, remote desktop tools have become vital business enablers, but due to their pervasiveness on corporate networks they have become a popular entry point for cyber criminals.

If successfully exploited, remote access tools can provide hackers with a direct pathway into a system or network, and once access is gained attackers can move laterally within the network, escalating privileges and maintaining persistence.

In an investigation into which remote desktop tools are targeted the most, Jonathan Tanner, senior security researcher at Barracuda Networks, explained that remote desktop software poses a particular challenge to IT teams to secure.

“Among the security challenges facing IT teams implementing remote desktop software is that there are many different tools available, each using different and sometimes several ports to operate.”

Tanner said Virtual Network Computing (VNC) technology was by far the most targeted remote desktop tool in the past year, accounting for 98% of the malicious traffic across all remote desktop specific ports.

VNC is a cross-platform tool that uses the RFB protocol to allow users and devices to connect to servers regardless of the operating system (OS). VNC underpins Apple’s remote desktop and screen sharing solutions, for example, as well as being used extensively in critical infrastructure, another growing target for cyber attacks.

Over 99% of the attack attempts leveraging VNC were aimed at HTTP ports, and the other 1% targeted the transfer control protocol (TCP). Tanner suggested this is probably due to the fact that HTTP does not require specific authentication, unlike TCP. 

The lion’s share of the VNC-based attacks observed by Barracuda Networks attempted to brute force weak and reused passwords. Some VNC offerings have an eight-character limit for passwords, the study noted, which makes cracking the password significantly easier for attackers.

RDP is the preferred choice for large-scale network attacks

The second most targeted remote desktop tool was the Remote Desktop Protocol (RDP), a secure network network communication protocol developed by Microsoft.

Barracuda found RDP accounted for approximately 1.6% of the attempted attacks it detected against remote desktop tools in the last year. 

Although VNC-based tools account for far more attempted attacks by volume, Barracuda’s analysis found larger attacks against networks and data are more likely to involve RDP.

These attacks will often result in the deployment of malware as part of a ransomware or cryptomining attack, or leverage vulnerable machines in a DDoS attack.


The security firm found around 15% of the attempted attacks on RDP systems involved an obsolete cookie, suggesting this could be a tactic employed by hackers to identify older and more vulnerable versions of RDP software for further exploitation.

Like VNC, most RDP tools are hit with credential-based attacks, yet there have also been a number of severe vulnerabilities affecting RDP in recent years.

For example, CVE-2018-0886 is a remote code execution vulnerability affecting the credential security support provider (CredSSP) used for RDP authentication.

Despite the variety of high risk RCE vulnerabilities affecting the protocol, most exploit attempts launched against RDP were denial-of-service vulnerabilities, which accounted for 9% of the traffic observed.

The investigation also noted that RDP has been used in Microsoft Support vishing attacks that try to convince victims that their machine is experiencing technical issues that require RDP access to be fixed.

Cyber criminals were also found selling vulnerable or cracked RDP instances for other hackers to use in attacks on underground marketplaces, for relatively modest prices of a few dollars per instance.

Solomon Klappholz
Staff Writer

Solomon Klappholz is a Staff Writer at ITPro. He has experience writing about the technologies that facilitate industrial manufacturing which led to him developing a particular interest in IT regulation, industrial infrastructure applications, and machine learning.